I have a D500. One thing to check are the a1: AF-C Priority Selection a2: AF-S Priority Selection. Set both of those to Focus. If they are set to Release you can take the photo even if your subject is out of focus. If those are set to Focus, the subject must be in focus before you can release the shutter.

Your flash may have had no effect if you were too far away from the main subject. What was the camera to subject distance?

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What you're saying about the 55mm lens on different cameras is nonsense. That's not what I was talking about.

You're not wasting the utilization of a FF lens on a non FF body. Just use the lens that has the focal length you need. I have both FF and cropped sensor Nikon cameras and lenses. I'll use the FF lenses on both the FF and cropped sensor cameras.

Having a cropped sensor camera for landscape photography can be good. You'll be using a wider angle lens to obtain the same field of view as a full frame camera. By using a wider angle lens you're getting more depth of field. For example a 35mm lens on a cropped sensor camera is producing roughly the same field of view and perspective as a 50mm lens on a full frame camera. The 35mm has greater depth of field than the 50mm.

I got the Tamron 10-24mm F/3.5-4.5 Di II VC HLD for my Nikon D500. The reviews I read stated that it's the best ultra wide angle zoon lens for cropped sensor cameras. It's very sharp and has vibration compensation. I think Canon is the only other company that has stabilized ultra wide angle zoom lenses. The Tamron is also weather sealed.

I rented the Nikon Z6 II for two weeks. I did not use the FTZ adapter so I can't comment on that. I was very impressed with the camera. I like the ergonomics. Nikon puts a lot of thought into the operation of the camera. I did some studio photography during that time. The eye detection AF worked great and picked up on the model's eyes really well. I did some landscape photography also. I think the Z6 III or Z7 III will probably be coming out very soon. I'm going to wait a little longer. I will buy a Z6 III if it materializes.

This is cryptic. I thought you were talking about your SB-400.

Check that the ready light on the back of the flash is on. Also, has the flash been unused for a long time? The manual for my Nikon SB-700 flash states that the flash should be fired a few times every month to refresh the capacitor. Apparently, it's possible that the capacitor will not fully charge if the flash has been unused for a long time.

You've gotten great advice on tripods. I would like to make a ballhead recommendation. Acratech has a unique ballhead design. The ball is actually open at the bottom. It allows any dust and debris to clear away instead of being trapped in a ballhead socket. They are very lightweight for their load capacity. This is my Acratech ballhead on my Manfrotto 055 carbon fiber tripod..

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I'm waiting on the Z6 III. I don't want 45MP. The 24 or 33MP of the new Z6 III is more than enough.

Heloicoils can be used to repair stripped out threads. You drill a larger hole and get a tap for screw thread inserts. There's a tool that's used to install the helicoil. The tang on the helicoil is then punched out.

A standard 3/8-16 thread tap uses 5/16 (.312) diameter drill
A 3/8=16 helicoil tap used a size X (.397) diameter drill

I work in a machine shop. You can get bottoming taps that have a much shorter lead than plug taps.

I was sitting at work programming and decided to open UHH to read the posts. I generally don't suspect that someone has dragged out an old post so I don't start looking at dates closely. Generally, the questions there are all current. I don't know the reason why someone would drag out one of their old posts. I'll look at the dates closely next time and skip any like this.

Explain yourself. I don't know what the heck you're talking about. What is it that I dragged up? I opened UHH just now and saw this. It's possible that I gave similar advice in 2011. I've had two D7000's and I'm familiar with it so I gave advice. I didn't not look at when the OP posted this. It looked like a valid question so I answered it.

The D3xxx and D5xxx series Nikons have a pentamirror viewfinder. If you go to a D7xxx series or higher Nikon you get a superior pentaprism viewfinder. The glass prism inside give a larger, slightly larger view through the viewfinder. It helps with composition. I had two D7000s. I only sold them because I purchased two D500s.

Advantages of the D7000 over the D5100
1) Pentaprism viewfinder rather than pentamirror viewfinder
2) Dual command dials
3) Dual memory card slots
4) U1 and U2 memory banks on mode dial
5) Superior AF module (Multi-CAM 4800DX in D7000 as opposed to Multi-CAM 1000 in D5100)
6) 39 autofocus points and 9 cross point types in D7000 as opposed to 11 autofocus points and 1 cross point type
7) Has built-in autofocus motor